Genetic Engineering of Lymphangiogenesis in Skin Does Not Affect Blood Pressure in Mouse Models of Salt-Sensitive Hypertension.

BACKGROUND: Recent studies have indicated that sodium storage is influenced by macrophages that secrete VEGF-C (vascular endothelial growth factor) during salt stress thus stimulating lymphangiogenesis, thereby acting as a buffer against increased blood pressure (BP). We aimed to explore the role of dermal lymphatics in BP and sodium homeostasis. Our hypothesis was that mice with reduced dermal lymphatic vessels were more prone to develop salt-sensitive hypertension, and that mice with hyperplastic vessels were protected. METHODS: Mice with either hypoplastic (Chy), absent (K14-VEGFR3 [vascular endothelial growth factor receptor 3]-Ig), or hyperplastic (K14-VEGF-C) dermal lymphatic vessels and littermate controls were given high-salt diet (4% NaCl in the chow), deoxycorticosterone acetate (DOCA)-salt diet and 1% saline to drink or nitric oxide blocker diet L-NG-nitro arginine methyl ester (followed by high salt diet). BP was measured by telemetric recording, and tissue sodium content by ion chromatography. RESULTS: In contrast to previous studies, high salt diet did not induce an increase in BP or sodium storage in any of the mouse strains investigated. DOCA-salt, on the other hand, gave an increase in BP in Chy and K14-VEGFR3-Ig not different from their corresponding WT controls. DOCA induced salt storage in skin and muscle, but to the same extent in mice with dysfunctional lymphatic vessels and WT controls. Lymph flow as assessed by tracer washout was not affected by the diet in any of the mouse strains. CONCLUSIONS: Our results suggest that dermal lymphatic vessels are not involved in salt storage or blood pressure regulation in these mouse models of salt-sensitive hypertension.

High-Salt Diet Causes Expansion of the Lymphatic Network and Increased Lymph Flow in Skin and Muscle of Rats.

Objective- A commonly accepted pivotal mechanism in fluid volume and blood pressure regulation is the parallel relationship between body Na+ and extracellular fluid content. Several recent studies have, however, shown that a considerable amount of Na+ can be retained in skin without commensurate water retention. Here, we asked whether a salt accumulation shown to result in VEGF (vascular endothelial growth factor)-C secretion and lymphangiogenesis had any influence on lymphatic function. Approach and Results- By optical imaging of macromolecular tracer washout in skin, we found that salt accumulation resulted in an increase in lymph flow of 26% that was noticeable only after including an overnight recording period. Surprisingly, lymph flow in skeletal muscle recorded with a new positron emission tomography/computed tomography method was also increased after salt exposure. The transcapillary filtration was unaffected by the high-salt diet and deoxycorticosterone-salt treatment, suggesting that the capillary barrier was not influenced by the salt accumulation. A significant reduction in lymph flow after depletion of macrophages/monocytes by clodronate suggests these cells are involved in the observed lymph flow response, together with collecting vessels shown here to enhance their contraction frequency as a response to extracellular Na+. Conclusions- The observed changes in lymph flow suggest that the lymphatics may influence long-term regulation of tissue fluid balance during salt accumulation by contributing to fluid homeostasis in skin and muscle. Our studies identify lymph clearance as a potential disease-modifying factor that might be targeted in conditions characterized by salt accumulation like chronic kidney disease and salt-sensitive hypertension.

Lymphangiogenesis Facilitates Initial Lymph Formation and Enhances the Dendritic Cell Mobilizing Chemokine CCL21 Without Affecting Migration.

OBJECTIVE: Lymphatic vessels play an important role in body fluid, as well as immune system homeostasis. Although the role of malfunctioning or missing lymphatics has been studied extensively, less is known on the functional consequences of a chronically expanded lymphatic network or lymphangiogenesis. APPROACH AND RESULTS: To this end, we used K14-VEGF-C (keratin-14 vascular endothelial growth factor-C) transgenic mice overexpressing the vascular endothelial growth factor C in skin and investigated the responses to inflammatory and fluid volume challenges. We also recorded interstitial fluid pressure, a major determinant of lymph flow. Transgenic mice had a strongly enhanced lymph vessel area in skin. Acute inflammation induced by lipopolysaccharide and chronic inflammation by delayed-type hypersensitivity both resulted in increased interstitial fluid pressure and reduced lymph flow, both to the same extent in wild-type and transgenic mice. Hyperplastic lymphatic vessels, however, demonstrated enhanced transport capacity after local fluid overload not induced by inflammation. In this situation, interstitial fluid pressure was increased to a similar extent in the 2 strains, thus, suggesting that the enhanced lymph vessel area facilitated initial lymph formation. The increased lymph vessel area resulted in an enhanced production of the chemoattractant CCL21 that, however, did not result in augmented dendritic cell migration after induction of local skin inflammation by fluorescein isothiocyanate. CONCLUSIONS: An expanded lymphatic network is capable of enhanced chemoattractant production, and lymphangiogenesis will facilitate initial lymph formation favoring increased clearance of fluid in situations of augmented fluid filtration.